High coercivity, high energy product permanent magnet materials are needed for different practical magnetic circuit designs employed in various microwave/millimeter wave devices as for example, traveling wave tubes (TWT's), cross-field amplifiers (CFA's), backward wave oscillators (BFO's), klystrons, magnetrons, carcinatrons, fixed and/or tunable frequency YIG filters, etc. The magnetic materials are also of importance in sensitive gyroscopes, accelerometers and various electromechanical devices.
Unfortunately, the best commercially available magnets today such as the rare earth SmCo.sub.5 magnets are not capable of meeting the remanence and energy product requirements of the aforementioned devices. That is, it is desirable to have materials with energy products (BH).sub.max in excess of 30 MGOe. The currently commercially available SmCo.sub.5 based magnets have values of (BH).sub.max that range from 18 to 24 MGOe and a rather high reversible temperature coefficient (RTC) of magnetization of -0.044 percent/C.
Recently, as reported in the article "New Type Rare Earth Cobalt Magnets with an Energy Product of 30 MGOe", by T. Ojima, S. Tomizawa, T. Yoneyama and T. Hori, Japan J. Appl Phys, Vol. 16, 1977 page 671, an optimized multicomponent alloy has been made that has yielded an energy product of 30 MGOe. This alloy has the composition Sm.sub.2 Cu.sub.1.6 Zr.sub.0.16 Fe.sub.3.3 Co.sub.12. While this Sm.sub.2 Co.sub.17 based alloy has an improved energy product as compared to SmCo.sub.5 based materials, its coercivity H.sub.c of about 6.5 kOe is lower than the H.sub.c of about 9 to 10 kOe attained in SmCo.sub.5 based compounds. This lower coercivity results in a non-linear second quadrant B vs H demagnetization curve that gives the alloy less desirable dynamic operating characteristics than SmCo.sub.5. The SmCo.sub.5 has a linear B vs H demagnetization characteristic with the linearity persisting well into the third quadrant. This permits a transient demagnetizing field in excess of H.sub.c to be applied and yet have the material recoil to an induction value B close to Br, the remanent field, on removal of the demagnetizing field. Such a linear characteristic also permits one to work with disk-like geometries, that is, low aspect ratios, and still maintain full magnetization of the material. The new alloy Sm.sub.2 Cu.sub.1.6 Zr.sub.0.16 Fe.sub.3.3 Co.sub.12 does not have this desirable property.